The present application claims priority under 35 U.S.C. xc2xa7119 of German Patent Application No. 199 28 753.8, filed on Jun. 23, 1999, the disclosure of which is expressly incorporated by reference herein in its entirety.
1. Field of the Invention
The present invention relates to a roll of the type used for smoothing paper webs. The roll has a hard roll core which can be a metal and an outside surface utilizing an elastic covering layer. The covering layer may be an elastic matrix material. Furthermore, the invention is directed to a process for producing such a roll.
2. Discussion of Background Information
Elastic rolls of this kind are used, for example, in the satining of paper webs. In such cases, one elastic roll forms, in each case together with a hard roll, a press gap through which the paper web to be treated is guided. The hard roll typically has a very smooth surface made, for example, of steel or chilled cast iron and is responsible for the smoothing of that side of the paper web facing it. The elastic roll acting on the opposite side of the paper web effects a homogenizing and compacting of the paper web in the nip. The size of the rolls can typically range from lengths of approximately 3 to approximately 12 m and the diameters can vary from approximately 450 to approximately 1500 mm. Moreover, they can withstand line forces of up to approximately 600 N/mm and compressive stresses of up to approximately 130 N/mm2.
As the trend in paper manufacturing is on performing satining in an online operation, i.e. towards guiding the paper web exiting a paper machine or coating machine directly through a paper smoothing apparatus (e.g., a calender), higher demands than were previously made are put on the rolls of the smoothing apparatus. This is particularly true with regard to temperature resistance. Further, as a result of the high transportation speeds of the paper web required in online operation and the high rotation speeds of the calender rolls associated with this design, its nip frequency, that is the frequency with which the covering is compressed and relieved of its load again, is increased. This in turn leads to increased roll temperatures. However, these higher temperatures which arise in online operations, lead to problems which can lead to the destruction of the plastic coatings in conventional elastic rolls.
On the one hand, conventional plastic coatings may withstand maximum temperature differences of around approximately 20xc2x0 C. over the width of the roll. On the other hand, the plastics which are conventionally used for the coating have a substantially higher coefficient of thermal expansion than the conventionally used steel rolls or chilled cast-iron rolls. Accordingly, due to an increase in temperature, high axial stresses occur between the steel roll or the chilled cast-iron roll and the plastic coating associated with it. Additionally, so-called hot spots, at which a peeling or even a breaking open of the plastic layer occurs, often arise due to these high stresses in conjunction with hot regions occurring particularly in spot-form.
These hot spots occur, in particular, when in addition to the mechanical stresses and the relatively high temperature, crystallization spots exist in the form of, for example, defective adhesive bonds, deposits or above-average recesses in the elastic coating. These may be, for example, due to creases or foreign bodies on the paper web. In such cases, the temperature at the crystallization spots can increase from a normal temperature in the range of approximately 80xc2x0 C. to approximately 90xc2x0 C. to more than approximately 150xc2x0 C. Accordingly, this can cause the above-mentioned destruction of the plastic layer to occur.
The present invention provides a process for producing a roll of the above mentioned type. Moreover, the invention is also directed to a corresponding roll. The roll of the invention is designed to withstand the formation or occurrence hot spots.
The invention is therefore directed to a roll which utilizes an elastic covering layer which is rotationally fixedly, but longitudinally displaceably arranged on the roll core. Moreover, the invention concerns a process of making a roll in which the elastic covering layer is applied to be longitudinally displaceable, but rotationally fixed to the roll core.
As a result of the elastic covering layer being arranged in accordance with the invention, i.e., longitudinally displaceably on the roll core, a situation is achieved in which none or very little longitudinal stresses occur between the roll core and the elastic covering layer. This will be the case even when the elastic roll-heats up, for example, such as when in operation.
This design allows the roll to heat up such that the elastic covering layer expands in an axial direction more than the roll core due to the higher coefficient of thermal expansion. However, the longitudinal displaceability of the covering layer, only leads to a relative movement occurring between the elastic covering layer and the roll core in an axial direction. In this design, either the two ends of the elastic covering layer can be axially displaced in opposite directions relative to the roll core or an asymmetrical longitudinal displacement of the elastic covering layer on the roll core can be allowed to occur. Depending on the different coefficients of thermal expansion and the temperatures which result, the relative displacement between the covering layer and the roll core can, for example, amount to around approximately 5 to approximately 50 mm, and commonly approximately 10 to approximately 20 mm.
In a roll designed in accordance with the invention, there is a stress-free connection between the elastic covering layer and the roll core. Accordingly, this design leads to a reduction in hot spots. Further, the risk of occurrence of a peeling of the covering layer from the roll core is significantly reduced and/or eliminated entirely.
By utilizing a rotationally fixed arrangement of the elastic covering layer on the roll core, it is ensured that, in operation, the covering layer is rotated securely together with the roll core as one unit. This ensures a uniform quality of the web of material which is to be smoothed.
According to one aspect of the invention, the elastic covering layer is disposed free from play on the roll core, in particular in force fit. A separation layer is preferably provided between the elastic covering layer and the roll core. This can, in particular, reduce the friction between the elastic covering layer and the roll core. This separation layer can advantageously include silicone and/or an essentially monomolecular layer and/or a corrosion- inhibiting or corrosion-preventing material.
As a result of the elastic covering layer being disposed free from play, e.g., in a force fit relationship, it is ensured that this layer lies positively over its whole circumference against the surface of the roll core. This is particularly important in a smoothing operation and when a relatively high mechanical load is placed on the covering layer. Any compression and/or crease formation in the covering layer, which can lead to a reduction in the quality of the treated material web, is thus prevented. Moreover, by utilizing a separation layer, for instance, the friction between the elastic covering layer and the roll core is reduced. Therefore, when the roll heats up, the desired longitudinal displacement can occur between the covering layer and the roll core.
However, it should be noted that the thinner the separation layer is designed here, the tighter the seating of the covering layer on the roll core. Moreover, due to the longitudinally displaceable support of the elastic covering layer on the roll core, it is generally possible for moisture to penetrate between the elastic covering layer and the roll core. This can allow for corrosion to arise on the metallic roll core. Accordingly, in an effort to prevent this, the separation layer can advantageously be formed from a corrosion-inhibiting or corrosion-preventing material.
The rotational fixation and simultaneous longitudinal displaceability of the elastic covering layer on the roll core can be advantageously achieved by rotational fixation and guide elements provided on the surface of the roll core and by counter-elements cooperating with these provided on the elastic covering layer. For example, one or more longitudinal guides extending essentially in an axial direction can be provided in and/or on the elastic covering layer. In particular, these can be in and/or on the radially inner surface of the elastic covering layer. Additionally, engaging elements, in particular, pin-like engaging elements, can be provided on the surface of the roll core so as to engage into them. In the same way, the longitudinal guides can be provided on the roll core while the engaging elements are provided on the elastic covering layer.
In one design, slot-like longitudinal guides and the pin-like engaging elements which engage into them provide for a simple rotational fixation with a simultaneous longitudinal displaceability of the elastic covering layer on the roll core. Generally, however, other designs are also possible which can achieve a rotational fixation with simultaneous longitudinal displaceability.
In accordance with another embodiment of the invention, one or more fiber layers are embedded in the matrix material of the elastic covering layer. Depending on the fiber material, the physical properties of the elastic covering layer can be preset by an embedding of the fiber layers. For example, by embedding fibers with a rigidity higher than that of the matrix material, the total rigidity of the elastic covering layer can be increased. In addition, the thermal conductivity of the elastic covering layer can be substantially increased over that of a covering layer of pure matrix material. Moreover, this can be accomplished by selecting fibers of high thermal conductivity. This can be particularly advantageous in the effort to improve the dissipation of excess heat.
Preferably, the fiber layers are formed at least partially by fiber bundles running obliquely to the surface of the roll core. These fiber layers can particularly include crossed fiber bundles. By utilizing crossed fiber bundles, a crossed assembly is created such that torsion of the elastic covering layer is largely avoided. Further, as the elastic covering layer in a roll designed in accordance with the invention is not fixedly connected to the surface of the roll core, any torsion of the freely displaceable covering layer is generally feasible. For this reason, the elastic covering layer should preferably be designed so that any torsion of the covering layer is counter-acted.
Accordingly, the elastic covering layer can include a radially outer functional layer and a radially inner connection layer to connect the functional layer with the roll core. As a result of this two separate layer design, these layers can each be adapted in optimum fashion to their relevant tasks. It is possible, for example, for the radially outer functional layer to have a higher elasticity than the radially inner connection layer. Moreover, the latter can have, in turn, for example, a higher rigidity in order to be able to reliably provide the rotational fixation to the roll core.
Advantageously, the invention provides that the fiber content of the covering layer can vary, in particular, decrease radially from the inside to the outside. Thus, the fiber content in the radially outer region of the covering layer can preferably essentially be equal to zero.
As a result of the variation in the fiber content of the covering layer radially from the inside to the outside, the covering layer can have a coefficient of thermal expansion which is also different in a radial direction from the inside to the outside according to the fiber content. This is because the matrix material usually has a much higher coefficient of thermal expansion than the fiber material used. Accordingly, this means that the resulting coefficient of thermal expansion of the matrix material permeated with fibers is dependent on both the coefficient of thermal expansion of the matrix material and that of the fibers. Thus, the more fibers that are embedded in the matrix material, the more the resulting coefficient of thermal expansion approaches the coefficient of thermal expansion of the fibers used. In this way, it is possible to adjust the coefficient of thermal expansion of the radially inner region of the covering layer so that it has the same order of magnitude as the coefficient of thermal expansion of the roll core. Therefore, when the roll heats up in operation, the radially inner region of the covering lay-c can thus only expand slightly more than the roll core so that a relatively low relative displacement arises between the elastic covering layer and the roll core.
However, as a high fiber content also substantially increases the rigidity of the covering layer, the fiber content in the radially outer regions of the covering layer must be chosen to be lower. Otherwise, the surface of the roll may be too hard and may not be suitable for satining. By utilizing a fiber content within the covering layer which decreases radially towards the outside and in particular substantially continuously radially towards the outside, a situation can be achieved in which when the roll heats up, the longitudinal stresses which occur inside the covering layer and which are due to the different thermal expansions of the different regions are at no point so large that a peeling or destruction of the covering layer occurs.
In order to produce an elastic roll in accordance with the invention, the elastic covering layer is longitudinally displaceably, but rotationally fixedly applied onto a roll core. For example, the elastic covering layer can be shrunk, e.g. shrunk fit, onto the roll core so that a press fit arrangement of the elastic covering layer on the roll core is achieved.
Moreover, a separation layer can be applied prior to the application of the elastic covering layer onto the roll core. Accordingly, this can be performed, in particular, to reduce friction between the covering layer and the roll core.
However, any conventional method can be utilized in which the elastic covering layer is applied and/or installed to the roll core rotationally fixedly as long as it is also longitudinally displaceable and/or, in particular, free from play. For example, the roll can be made by pushing a prefabricated, tube-shaped covering layer onto the roll core.
The invention provides that a plurality of fibers can, for example, be wound on the roll core, in particular in multiple fiber layers one over the other, to produce the covering layer. In a similar way, it is possible to wind the fibers onto a coil former, in particular, onto a cylindrical coil former, which is pulled out of the wound covering layer at the end of the winding process.
The fibers can in each case be wound in the form of one or more fiber bundles and/or fiber rovings and/or fiber fleeces. In this case, it may be advantageous here for the fibers to be enveloped by the matrix material, in particular to be drawn through a matrix bath, prior to the winding. Generally, however, it is also possible for the fibers to be wound on in an essentially dry state and for the matrix material to be applied to them during or after winding, in particular for them to be completely embedded in the matrix material.
The invention therefore provides for a roll for smoothing of a material web comprising a hard roll core having an outside surface, and an covering layer comprising an elastic matrix material and disposed on the outside surface, wherein the covering layer is rotationally fixed and longitudinally displaceable on the hard roll core. The material web may be a paper web. The hard roll core may comprise a metal. The covering layer may be rotationally fixed and longitudinally displaceable relative to the outside surface of the hard roll core. The covering layer may comprise an inside diameter which substantially corresponds to an outside diameter of the hard roll core. The covering layer may be disposed on the hard roll core so as to be free from play. The covering layer may be force fit onto the hard roll core. The roll may further comprise a separation layer disposed between the outside surface of the hard roll core and the covering layer. The separation layer may reduce friction between the covering layer and the outside surface of the hard roll core. The separation layer may comprise silicone. The separation layer may comprise an essentially monomolecular layer. The separation layer may comprise one of a corrosion-inhibiting material and corrosion-preventing material. A coefficient of thermal expansion of the covering layer may be greater than a coefficient of thermal expansion of the hard roll core.
The roll may further comprise a plurality of guide elements engaging each of the covering layer and the hard roll core, the guide elements being positioned to guide the longitudinal displacement of the covering layer and to rotationally fix the covering layer of the hard roll core. The roll may further comprise at least one guide element disposed on the surface of the hard roll core, and at least one counter-element disposed on the covering layer, wherein the at least one guide element is positioned to engage the at least one counter-element disposed on the covering layer, and wherein the covering layer is longitudinally displaceable and rotationally fixed on the hard roll core via engagement of the at least one guide element and the at least one counter-element. The at least one counter-element may be disposed on a radially inner surface of the covering layer, and comprises a longitudinal guide which extends essentially in an axial direction, and wherein the at least one guide element comprises a pin-like engaging element that is arranged to project from the surface of the hard roll core and to engage the longitudinal guide disposed on the covering layer. At least one longitudinal guide may be disposed on the surface of the hard roll core and at least one engaging element is disposed on the covering layer. The covering layer may comprise at least one fiber layer which is embedded in the elastic matrix material. The at least one fiber layer may comprise a plurality of fiber layers, and wherein at least one of the plurality of fiber layers is formed at least partially by fiber bundles. The fiber bundles may be arranged to run obliquely relative to the surface of the hard roll core. The fiber bundles may comprise crossed fiber bundles. The covering layer may comprise a radially outer functional layer and a radially inner connection layer, and wherein the connection layer connects the functional layer to the hard roll core. At least one of the connection layer and the functional layer comprises a fiber content. The connection layer and the functional layer may comprise a fiber content. The fiber content of the connection layer may be higher than the fiber content of the functional layer. A fiber content in a radially outer region of the connection layer may be essentially equal to a fiber content of a radially inner region of the functional layer. The fiber content may be quantified in one of number of fibers, volume of fibers and percentage of fibers.
The covering layer may comprise a fiber content, and wherein the fiber content of the covering layer varies radially outwardly. The fiber content of the covering layer may decrease radially outwardly. The fiber content in a radially outer most region of the covering layer may be essentially equal to zero. The fiber content may comprise fiber layers. The fiber layers may comprise at least one of glass, aramide, and carbon fibers. The elastic matrix material may comprise a plastic. The plastic may comprise one of a thermosetting plastic and a thermoplastic. The elastic matrix material may comprise a resin and a hardener combination.
The invention also provides for a process for making a roll for smoothing a material web, the roll comprising a hard roll core having an outer surface and an elastic covering layer which includes an elastic matrix material, the method comprising applying the elastic covering layer on the outer surface of the hard roll core, wherein the elastic covering layer is rotationally fixed and longitudinally displaceable on the outside surface of the hard roll core. The material web may be a paper web. The hard roll core may comprise a metal. The applying may comprise shrinking the covering layer onto the hard roll core. The applying may comprise shrink fitting the covering layer onto the hard roll core.
The process may further comprise providing a separation layer between the elastic covering layer and the hard roll core, wherein the separation layer is adapted to educe friction between the covering layer and the hard roll core. The separation layer may be provided prior to the applying of the elastic covering layer. The process may further comprise forming the elastic covering layer with a plurality of fibers wound onto a cylindrical coil former. The plurality of fibers may comprise multiple fiber layers wound one over another. The process may further comprise forming the elastic covering layer with a plurality of fibers wound onto the hard roll core. The plurality of fibers may comprise multiple fiber layers wound one over another. The at least one of the multiple fiber layers may comprise at least one of a fiber bundle, a fiber roving, and a fiber fleece, wherein the fiber roving comprises a plurality of adjacent fibers of the same kind. At least one of the multiple fiber layers may comprise at least one of a fiber bundle, a fiber roving, and a fiber fleece, wherein the fiber roving comprises a plurality of adjacent fibers of the same kind. The elastic matrix material may envelope the plurality of fibers. The plurality of fibers may be drawn through a matrix bath prior to winding. The elastic matrix material may envelope the plurality of fibers. The plurality of fibers may be drawn through a matrix bath prior to winding. The winding of the plurality of fibers may further comprise winding the plurality of fibers onto the hard roll core in an essentially dry state.
The process may further comprise applying the elastic matrix material to the plurality of fibers in the essentially dry state during winding, wherein the fibers are completely embedded in the matrix material. The forming may comprise applying the elastic matrix material to the plurality of fibers in the essentially dry state after winding, wherein the fibers are completely embedded in the matrix material. The plurality of fibers may be wound in one of an oblique manner and a crossed manner. The plurality of fibers may comprise one of glass, aramide, and carbon fibers. The plurality of fibers may be wound in one of an oblique manner and a crossed manner. The plurality of fibers may comprise one of glass, aramide, and carbon fibers.